Ethylene propylene rubbers (including diene rubbers) are commercially produced in a gas phase process above the softening or sticking temperature of the polymer product by using an inert particulate material such as carbon black, silica, clay or talc, as disclosed in U.S. Pat. No. 4,994,534. The inert particulate material serves to make the forming bed of polymer fluidizable. Hence, it is required to prevent agglomeration of the bed in the gas phase reactor. The preferred inert particulate material is carbon black. Carbon black is preferred because it is most often included in molded or extruded article by an end user.
Presently, the catalyst of choice in gas phase polymerization is a vanadium catalyst (e.g., vanadium acetylacetonate supported on silica), though a titanium catalyst can be employed. However, the use of a vanadium catalyst does not afford latitude for producing a wide variety of EPR differing in amounts of individual monomers comprising them and various molecular weights and/or molecular weight distribution. Solution, slurry, and bulk EPR processes, which do not employ inert particulate material in the polymerization, employ a metallocene catalyst for these purposes.
However, in gas phase production requiring an inert particulate material, such as carbon black, attempts to use a metallocene catalyst, it has been discovered that the carbon black has a strong poisoning effect on the metallocene catalyst. That is, the poisoning effect of carbon black (CB) consumes cocatalyst such as MAO or modified MAO (MMAO) and decreases catalyst activity. Hence, more aluminoxane is needed in order to obtain sufficient metallocene activity and the catalyst cost is substantial.
Therefore, there exists, a need for a passivation process which alleviates the poisoning effects of inert particulate materials such as carbon black on metallocene catalysts so that catalyst activity increases and provides a reduction in the high cost of using aluminoxane such as methylaluminoxane (MAO) cocatalyst in the production of EPR.